The photoluminescence of a single nickel-nitrogen NE8 color center in a diamond nanocrystal is investigated at room temperature under pulsed excitation by scanning confocal optical microscopy. Photon arrival times are analyzed in terms of the temporal intensity correlation function. Antibunching at short times and bunching behavior for longer times is observed, associated with sub- and super-Poissonian statistics, respectively. The behavior is interpreted by a 'on-off' state model, and transition rates between these two states are inferred from intensity correlation measurements realized at different excitation powers. NE8 color center photoluminescence quantum yield is evaluated to be 65%, a value higher than achieved for a nitrogen-vacancy color center, which is, up to now, the most practical single emitter to build a reliable single-photon source at room temperature.